Arun buys toffees at 6 for a rupee. How many toffees per rupee should he sell to gain 20%?

Introduction:
Convert the buying rate to cost per toffee, increase by 20% to get selling price per toffee, then invert to get the number per rupee.

Given Data / Assumptions:

• Buy: 6 for Rs 1 ⇒ CP per toffee = Rs 1/6
• Desired gain = 20%

Concept / Approach:
SP per toffee = 1.20 * (1/6) = 1/5. Then number per rupee = 1 ÷ (1/5) = 5.

Step-by-Step Solution:
CP per toffee = 1/6 rupeeSP per toffee = 1.2 * (1/6) = 1/5 rupeeToffees per rupee = 5

Verification / Alternative check:
On 5 toffees: SP = 1 rupee. CP for 5 = 5/6 rupee. Profit = 1 − 5/6 = 1/6 rupee = 20% of 5/6 rupee.

Why Other Options Are Wrong:
3, 4, 6: Do not correspond to a 20% gain on the given CP.can't be determined: Sufficient information exists.

Common Pitfalls:
Using difference in counts directly without converting to unit prices; miscomputing 20% increase.

Final Answer:
5